The Telescope Myth

[stevepenny]

Hi all,

Being new to the science and to the SGL please accept my apologies if this question has been asked repeatedly; but I am having difficulty wading through the various advice (myths) surrounding Telescopes.

For example; I'm told that a long focal length is good for planets in order to see the detail; but no good for deep sky objects due to a reduced field of view and 'shake'.

I'm also told that Dobsonians and are no good for astrophotography as they do not have an equitorial mount; but I have found one with a DSLR mount.

I have read that SCT's are superior to MCT's in terms of clarity, weight and price.....although it depends what you read.

Finally i'm told that aperture is everything (i.e. size matters) and that anything below 6" is of little use.

So i'm torn between a SkyLiner 200P FlexTube AUTO or an Evostar-120 (EQ5) 4.75" Refractor; or even perhaps a Skywatcher Explorer 200PDS with EQ-5 Mount and Dual-speed Focuser.

I have picked these because they probably represent my maximum budget in both catagories and will (may) allow me to keep the same scope when I take up the photography side (when I can afford it).

So what is it that I want? Well; I would like to see the planets in some detail i.e. the Jovian weather patterns and Saturn's rings; but also other galaxies and star clusters. It would be nice to be able to see the Flame Tree but I understand that this may not be likely. (I really want to be able to see the HHN but now know that this is probably only likely with photography).

So that's it really; I want it all but do not want to spend it all.....but any advice that can be given as to the choice of a good general purpose telescope that can be used for astrophotography would be appreciated.

Thanks in advance;

Steve in Aberdeen

[nightfisher]

I would suggest the 200 dob, it will be very good for planets lunar and lots of dso`s in time if you want to do astro photography you could get a decent mount and image with the same tube

[garethmob]

the 200p dob is really nice scope as nightfisher said, and it does come with a dslr mount, but watch out because you cant use the camera unless its on a EQ mount or a ALTAZ mount with a wedge. you can get scope rings and mount it on a dovetail but a heq5 would be the minimum for photogaphy

one thing to consider, you can get "reducers" that turn F8 or slower (the higher the number) scopes into faster (the closer to 0) scopes, so these then can be used a little better on the brighter DSO's althrough im not sure if the ones you mention would be in range. scopes 6" and lower are really really good scopes, i used my 6" dob more than the 8, and my new scope (the WO76) is even smaller again, with approiate eyepeices and barlow, other night i was looking at jupitor, 4 moons, bands, M31, a few glob clusters. and m101.

im going to assume (based on the flex tube) ur absolute budget is £460

now heres the fiddly part. the flex CANT be used on a eq mount as its very hard to balance it, so its a dob only, but u will near enough see everything on it

the evo 120, is primially a moon and planet scope but with a reducer it can bring it down to the AP player on the EQ mount it will be sort of ok but the mount will need to be tracked (have motors on it) so budget a set of motors as well (im not going to go into the synscan to no synscan debate but hopefully some one can answer that soon)

have you thought about somthing like this?

First Light Optics - Celestron Nexstar 102 SLT

First Light Optics - Skywatcher Startravel 102 SynScan AZ GOTO

it is an ALTAZ scope so DSO imaging is near enough off the table but you can mount the scope on a EQ mount at a later date, you can image plants, moon and even really bright DSO's but short exposures (due to field rotation) with a webcam (like the phillips) its also computer controled, so if your not too sure where things are it will help.

but as i said, full blown AP would be off the table till you can get a EQ mount

[g0ibi]

I love my new 200PDS on an EQ5 Pro, does all I want, planets,DSO's and astrophotography which I am just starting!

[brantuk]

Sounds like the advice you've taken on board is near enough all good. If you go the refractor route be sure of the differences between achro's and appo's. I have a 4.5" appo and it's superb.

Yes - if you intend imaging dso's then a good solid equatorial mount is paramount. You need to be able to align with the pole star so it will track accurately in a single plane (RA). Alt/az mounts (including dobs) don't do this - they track in RA and Dec and will restrict you're pics to planetary and moon due to star trailing.

Aperture generally is king as you say - whichever scope type you go for (Newtonian, Refractor, or Compound) the larger aperture you can handle (within budget) will give the more pleasing results. But bear in mind the larger you go the more solid and stable the mount/tripod needs to be.

To organise your thinking it may help to decide on what you want to see or image first, then pick the scope type to match requirements, then pick the matching mount type, then see if you can find a package or do a deal that combines everything. Bear in mind setup time, weight, portability, and storage area.

Hope that helps

[JamesM]

You might want to get hold of a copy of Steve Richards "Making Every Photon Count" (FLO £19.95) to help you understand the kit requirements of imagery and how they might differ from observing. It is also a very good instruction book in advising why you need certain kit to help you obtain they level of imaging that will meet your expectations. The most important advice is not to rush into any purchase till you know what you need and please keep asking any questions that might help with this cause.

Clear skies

James

[ronin]

Concerning the Dob with a DSLR connector, what you have is a newtonian with a DSLR connection, this newtonian is mounted on a dobsonian mount.

It is the mount that is not really suitable for astrophotography. The reason for the DSLR connector is that you can buy an HEQ5, get mounting rings and a dovetail and mount the scope bit on an equitorial and take pictures.

Photograophy is often done at prime focus, where the scope focuses. A long focal length means that this image is bigger then with a short focal length, Larger image means a bit dimmer so the exposure is longer, additionally the tracking has to be more accurate. So a short focal length has the advantage over a long focal length.

Planets are often bright so you can apply greater magnification and still see the detail, a long focal length means you get more magnification for the same eyepiece focal length. So a bit better for planets as they can accept greater magnification.

So no real myths, simple optics, mechanics and geometery.

You cannot have it all, get that understood, just about everyone getting into this wants to do everything and on a budget. I would suggest that you choose between visual and astrophotography first, then gear up for whichever one you decide on. I would say that if you were thinking of a 200P on an EQ5 for astrophotography that the EQ5 is too small.

[umadog]

I'll tell you what I think about these things. Probably some will disagree, but there we go

"I'm told that a long focal length is good for planets in order to see the detail; but no good for deep sky objects due to a reduced field of view and 'shake'."

It's true that a wide field of view is nice for DSOs. Some of them are very large and either won't fit in a small field or aren't framed well in it. It's not true that you need a long focal length for planets. There are barlow lenses and shorter focal length eyepieces (some with generous eye-relief) that will allow you to magnify as much as you need in any focal length. Heck, the Radian design actually incorporates a Barlow, which is how you get the very long eye relief even at eyepiece focal length of <10 mm. Finally, the "shake" depends on the mount. Shake is more of a problem with higher power stuff such as planets than DSOs.

"I'm also told that Dobsonians and are no good for astrophotography as they do not have an equitorial mount; but I have found one with a DSLR mount."

Yeah, but I wouldn't trust the manufacturers with everything... If a Dob is motor-driven then some simple photography becomes possible. If you have a good drive system then some reasonably good results can be obtained. However, you will work harder for worse results than a dedicated imaging rig could produce. You will have trouble with even moderately long exposures and not be able to do any long exposures. The mount is too wobbly for high quality stuff. Dedicated imaging scopes often come in very short focal lengths and don't need to have large aperture. So they aren't great for visual. Visual scopes and AP scopes have different requirements and what is optimal for one isn't for the other. You can do both AP and visual with same scope, particularly when you're starting out, but you need to prioritise which is more important to you.

"I have read that SCT's are superior to MCT's in terms of clarity, weight and price.....although it depends what you read."

I don't know. I suspect, however, that it depends as much on the optical quality as on the design. I'm told that designs where mirror motion is used for focusing are less good for AP because the focus has a tendency to slip.

"Finally i'm told that aperture is everything (i.e. size matters) and that anything below 6" is of little use."

Size is everything within reason. If you buy a 16" SCT a your first scope you will regret it (unless you can build an observatory in the back garden). Larger primary mirrors tend to have longer focal lengths which means narrower fields of view. If you like to see open clusters then this is no good. A 6" f/6 or 8" f/5 would give more pleasing views of the larger clusters. Even binos would be better for the really big stuff.

Scopes smaller than 6" do have lots of uses. Go look around the interweb for photography done with 3" refractors: amazing. Stephen O'Meara, who's one of the most experienced visual observers in the world, uses a 4" Televue Refractor. Google him. Here's the thing, though, the quality of the skies are more important that the size of the scope. O'Meara observes from Hawaii, where the gengeschien counts as light pollution. Most of the rest of us don't even know what the gengeschien is, because our skies are rubbish. I'd rather have a 6" scope in dark skies than a 25" somewhere light polluted. Seriously. The number of DSOs you can see and the detail you can see increases sharply over the first 10" of the aperture range. After that, it makes relatively less difference unless you start going to really big scope sizes. In light polluted skies the aperture will really help. If your skies are dark than it all looks pretty in almost any scope size. An 8" is an ideal size to get started with and may will be the last scope you'll ever want to buy.

"So i'm torn between a SkyLiner 200P FlexTube AUTO or an Evostar-120 (EQ5) 4.75" Refractor; or even perhaps a Skywatcher Explorer 200PDS with EQ-5 Mount and Dual-speed Focuser."

My suggestion is to go for the Dob now. Forget about AP for now. It's expensive and takes a lot of time. Get into AP later if you're still interested. There's logic to this: buy a second scope for AP in the future and keep the Dob. That way you can use the Dob to look at stuff whilst your fancy imaging rig is taking those 2 hour exposures. Then again, it's your money. If you're really set on AP go for the EQ-mounted Newt. I say that cautiously, however, I don't know how well that design works for AP. The probability of you wasting money is higher if you jump into AP straight away. There are lots of little odds and ends you'll need/want to buy and they add up in price. I think the financially astute option is to start with visual and spend a few months reading about AP in books. Eventually you'll know what's needed and won't be asking other people to tell you. When spending lots of money, it's never a good idea to rely on other people to tell you how to spend it.

"Well; I would like to see the planets in some detail i.e. the Jovian weather patterns and Saturn's rings; but also other galaxies and star clusters. It would be nice to be able to see the Flame Tree but I

understand that this may not be likely. (I really want to be able to see the HHN but now know that this is probably only likely with photography)."

Saturns rings are are easy: they're visible in large binos. A bigger scope really helps with Jupiter surface detail. The Flame Nebula needs dark skies more than a big scope. Here's what you can expect to see from somewhere dark with an 8" once you have some experience: http://www.deepskywatch.com/images/sketches/horsehead-flame-nebula-sketch.jpg

[brantuk]

Just FYI here's an image of the Flaming Star Neb taken with a less than 3" telescope - so size really depends on what you are doing and how you're doing it lol

Taken with my scope by a friend who (unlike me) knows what he's doing lol

[todd8137]

i can take pics with my 12"reflector on a dob mount

[umadog]

Yes, you can, and so can these guys: Obsession Telescopes / Imaging It is possible to get some rather good results. Better than most people will admit. It's just that it's more work and the results will never be as good as a dedicated setup. There are good reasons why hard-core imagers aren't using Dobs. As far as I know, very long exposures aren't possible in practice so you're always fighting the sensor's read-noise.

At the end of the day, Steve, you can just buy any of those scopes and you'll be fine. Toss a coin. If you take to the hobby then your first scope won't be your last. It is physically impossible for one scope to excel at everything, no matter what you spend. I know it seems like a big decision, but in reality you won't know what's suitable for you until you starting using it and learning and have made some mistakes.

Buy a good AP book, if you're serious about it. Photography is sufficiently complicated that learning it can not be done via an internet forum. You can always come here for advice, but you first need to do some research and learning. You'll be asking very different questions after that.

[stevepenny]

All,

Thank you all so much for your kind replies and advice. It will take me some time to read and digest it all but i'm sure it will point me in the right direction.

Steve

[Adrian]

If you are on a budget I would consider second hand through sites such as UK Astronomy Buy & Sell (U.K. Astronomy Buy & Sell) and the buy & sell section on this forum (once you have 50 posts and 1 month membership).

If you don't like a scope you won't lose much money selling it on compared to buying new - this is especially the case for achromatic refractors. Once you have a scope you will soon find out what you enjoy and so what scope would be best for you. And you won't have lost much (if any) of your budget.

I have used both sites to buy & sell and have not had a problem so far.

Also, try to visit an astronomy club - I visited my local one and found that I wasn't thrilled by pushing the big dob around (YMMV) so haven't considered that route and have stuck to EQ mounts. I also got to try out a refractor and a celestron 6SE.